Origin

This comes via Old French and Latin from Greek dialogos, from dialegesthai ‘converse with, speak alternately’: the formative elements are dia- ‘through, across’ and legein ‘speak’. The tendency in English is to confine the sense to a conversation between two people, perhaps by associating the prefix dia- with di-. Dia- is also found in diameter (Late Middle English) ‘the measure across’; diaphanous (early 17th century) ‘shows through’; diaphragm (Late Middle English) a barrier that is literally a ‘fence through’, and diaspora (late 19th century) a scattering across.